In connection with the above-referenced type of refiners, the inner portion of the feed zone the effect of centrifugal force on the supplied material is low. For this reason, the material supplied through the opening in the stationary refining element is generally not fed out sufficiently rapidly through the feed zone to the refining zone, which is located radially outward from the feed zone. As a result, the material can clog in the feed zone, which results in friction losses and non-uniform feeding, which in turn leads to deterioration in the pulp quality. For overcoming these problems, mechanical feeding devices of different types have been arranged in the feed zone, for example wings, blades, strips or the like. These devices, however, have not worked satisfactorily, particularly not when they have been designed so as to render the rotating refining means to reverse. It is thus often desired to be able to reverse the rotation of the refining means during pulp manufacture, since this can increase the life of the refining elements.